Tyre Pressure

[AbidK]

Hi

Wondering if anyone can help, my QP GTS tyre pressure sticker states 29psi and 32psi for the front and rears is this correct as it seems quite low to me?

 

[CatmanV2]

Sounds about right to me. My Ghibli is listed as 32. My GT manual indicates 31.9

C

 

[Sam McGoo]

Yeah that sounds correct.
Personally I run mine at 36psi for normal driving, as it helps even out the tyre wear a bit.

 

[Ebenezer]

My 4.2 QP is 32 all round.
Eb

 

[CatmanV2]

Yeah that sounds correct.
Personally I run mine at 36psi for normal driving, as it helps even out the tyre wear a bit.

That sounds quite high. I mean 20% up?

C

 

[AbidK]

Thanks Guys.

I just keep thinking the tyres are punctured when viewed at a certain angle whilst parked up.

 

[CatmanV2]

Thanks Guys.

I just keep thinking the tyres are punctured when viewed at a certain angle whilst parked up.

I've often thought that looking at some of my cars

C

 

[Zep]

Particularly on wide tyres, pressure is quite crucial. It’s what keeps the middle of the tyre on the road. Too low, it rides the sidewalls and wears the outer edges. Too high and it only wears the middle. How you drive also affect this. If you drive fast the centrifugal force acts on the tread, causing that to wear a bit more.

 

[Phil H]

If you drive fast the centrifugal force acts on the tread, causing that to wear a bit more.

Usually happens to me at the lights

 

[Felonious Crud]

iirc there was some past advice to inflate the tyres 2psi higher than the book says. Ringing bells for anyone else?

 

[DLax69]

iirc there was some past advice to inflate the tyres 2psi higher than the book says. Ringing bells for anyone else?

I find that around 50 psi, I can get up on two wheels in most turns:

 

[Gazcw]

I've often thought that looking at some of my cars

C

Ditto

 

[StuartW]

Remember that the ambient temperature can have a big impact when reading tyre pressures. If you check your tyres in the winter & your car is kept outside, they will read very low and once you drive and get up to temperature, there is a risk of having over inflated them.
The Stradale pressures from memory are 35 front and 33 rear when cold but in the winter months even in the garage, the TPMS will show a significantly lower reading

 

[CatmanV2]

Remember that the ambient temperature can have a big impact when reading tyre pressures. If you check your tyres in the winter & your car is kept outside, they will read very low and once you drive and get up to temperature, there is a risk of having over inflated them.
The Stradale pressures from memory are 35 front and 33 rear when cold but in the winter months even in the garage, the TPMS will show a significantly lower reading

P1V1T1=P2V2T2

This is why the 'cold pressure' temperature is sometimes mentioned

C

 

[Zep]

The whole cold pressure thing is interesting, it’s done to get a level of consistency and make it simple for Joe Public. Gas Laws state that the pressure for a fixed volume of gas is proportional to its temperature, as per Catman’s equation, which is great in theory and so cold temperatures are a perfectly reasonable way of setting the operating pressure of our tyres.

In practice, because there is a variable amount of moisture in the air in tyres and that moisture has a different relationship with temperature as well as affecting the rate at which the kinetic energy is converted into thermal energy (so tyre warm up) so it would be better to set the hot pressure, but this is a bit complicated for people who drive **** boxes.

A good example of this is my daily BMW, it monitors both pressure and temperature on its TPMS, and gives recommended pressures based on the temperature. To get any level of consistency (by consistency, I mean to get the hot temperature bang on because having it one PSI out messes with my COD) I have to set the pressures after a long drive with both the wheel and tyre up to temp. So the best way, if you are bothered by that sort of thing, is to set the temp cold, drive, check them hot, adjust them, drive it and see how it feels, find a good hot pressure and set it to that going forward. And yes, to do that you would have to be completely mad. Flibble.

 

[RodTungsten]

Crikey this forum straying into the realms of Gay -Lussac’s law. Anyone for the general gas equation to define the ideal/hypothetical state of our tyres?
Our Zoe shows higher temps by 3 or 4 degrees C on the sunny side of the car. Maybe I should go out and rotate it before the Wee Wonan departs.

 

[Sam McGoo]

That sounds quite high. I mean 20% up?

C

Yeah, quite possibly. But I've done this for many years on the Masser and my GTR before it.
A lot of my driving is spirited, I prefer how it feels when cornering and found it understeers less if pushing it. And like I said, it helps even out the wear a bit as the tyre spends less time on its shoulders.
The only real downside to be a slightly harsher ride on rough surfaces. In the Masser anything between 34-36 psi cold and I'm usually happy.
Obviously, if I was tracking it or in colder weather I'd adjust it.

 

[midlifecrisis]

And it all depends which kind of 'air' you put in...100% nitrogen anyone?

 

[Zep]

And it all depends which kind of 'air' you put in...100% nitrogen anyone?

Dry nitrogen would be more linear that straight air, but then you have different hot pressure compared to what was expected, so still better to set them hot. But you pay your money, etc etc.

 

[CatmanV2]

Dry nitrogen would be more linear that straight air, but then you have different hot pressure compared to what was expected, so still better to set them hot. But you pay your menus, etc etc.

I find it odd with mine that the two sensors on the right read lower than the ones on the left. Even if my digital gauge swears blind they are exactly the same.....

C